The overall objective of this proposal is to determine the cellular mechanisms underlying the age-dependent modulation of prefrontal cortical (PFC) interneuronal circuits. Such developmental regulation is highly relevant to the pathophysiology of schizophrenia since converging findings stress interneuron deficits during development as a potential basis for this disorder. However, the link between how an early developmental dysregulation of neural circuits affects the developmental trajectory of cortical interneuron maturation remains unknown. The PFC is a good site for studying the role of cortical inhibitory circuits, since the PFC plays an important role in working memory and decision-making, functions that become impaired in schizophrenia. Our recently published work and preliminary studies indicate that PFC interneuronal activity is enhanced after puberty. This postpubertal/late adolescent facilitation is thought to be related to the delayed maturation of the mesocortical dopamine system and the enhanced facilitation of glutamatergic drive onto these GABAergic interneurons. If during development, such interneuronal activity does not become enhanced, PFC inhibitory control will be altered at maturity. Such impairment would be important for the onset of PFC cognitive deficits during the periadolescent transition as observed in schizophrenia and certain psychiatric disorders. Our central hypothesis is that normal maturation of PFC GABA interneuronal function results from two concurrent late adolescent events: (i) augmentation of glutamatergic drive onto PFC interneurons; (ii) acquisition of postsynaptic Ca2+dependent signaling mechanisms that enable the increased interneuron response to dopamine. Thus, the rationale for the proposed work is that the developmental dysregulation of glutamatergic inputs to the PFC will be sufficient to alter the normal trajectory of prefrontal interneuronal function. Aim 1 will determine the cellular mechanisms that contribute to the developmental facilitation of PFC interneuronal activity. Aim 2 will determine the impact of the developmental facilitation of PFC interneuronal function on mesocortical-induced synchronous activity. Aim 3 will determine the anatomical origin of glutamatergic inputs that contribute to the late-adolescent facilitation of PFC GABA interneuron activity. Our prediction is that presynaptic facilitation of glutamatergic drive onto PFC interneurons dictates the normal maturation of dopamine control of PFC inhibitory transmission. Our results should lead to novel physiological and molecular strategies to target the presynaptic mechanisms underlying PFC interneuronal maturation that will increase cortical inhibitory transmission.